Characteristic mode analysis is a popular tool used in antenna design and the analysis of radiation mechanisms [1]}, [2]}, [3]}. The most common numerical implementation of characteristic modes is via method-of-moments (MoM) system matrices as proposed by Harrington and Mautz [4]}. As such, the characteristic mode decomposition was understood to be closely related – if not directly depending on [5]} – MoM [6]}, a procedure for constructing system matrices out of prescribed integro-differential operators [7]}. That this is not necessarily the case was recently presented in [8]}, where an algebraic link between the transition matrix [9]}, [10]} and an arbitrary system matrix was devised, referring back to the original, almost forgotten, definition of characteristic modes given by Garbacz which is based on the perturbation matrix [11]}.
